Protein kinases are a family of enzymes that catalyze phosphorylation of the hydroxyl groups of specific tyrosine, serine, or threonine residues in proteins. Typically, such phosphorylation can dramatically change the function of the protein and thus protein kinases can be pivotal in the regulation of a wide variety of cellular process, including metabolism, cell proliferation, cell differentiation, and cell survival. The mechanism of these cellular processes provides a basis for targeting protein kinases to treat disease conditions resulting from or involving disorder of these cellular processes. Examples of such diseases include, but are not limited to, cancer and diabetes.
Protein kinases can be broken into two types, protein tyrosine kinases (PTKs) and serine-threonine kinases (STKs). Both PTKs and STKs can be receptor protein kinases or non-receptor protein kinases. PAK is a family of non-receptor STKs. The p21-activated protein kinase (PAK) family of serine/threonine protein kinases plays important roles in cytoskeletal organization, cellular morphogenesis, cellular processes and cell survival (Daniels et al., Trends Biochem. Sci. 1999 24: 350-355; Sells et al., Trends Cell. Biol. 1997 7:162-167). The PAK family consists of six members subdivided into two groups: PAK 1-3 (group I) and PAK 4-6 (group II) which are distinguished based upon sequence homologies and the presence of an autoinhibitory region in group I PAKs. p21-Activated kinases (PAKs) serve as important mediators of Rac and Cdc42 GTPase function as well as pathways required for Ras-driven tumorigenesis. (Manser et al., Nature 1994 367:40-46; B. Dummler et al., Cancer Metathesis Rev. 2009 28:51-63; R. Kumar et al., Nature Rev. Cancer 2006 6:459-473).
Changes in the levels and activities of group 1 PAKs in particular, are frequently associated with human malignancies including, but not limited to bladder carcinoma, breast carcinoma, colorectal carcinoma, gastric carcinoma, glioblastoma, hepatocellular carcinoma, ovarian carcinoma and renal cell carcinoma, primary breast adenocarcinoma, squamous non-small cell lung cancer or a squamous head and necks cancer. (J. V. Kichina et al., Expert. Opin. Ther. Targets 2010 14(7):703) PAK1 genomic amplification at 11q13 was prevalent in luminal breast cancer, and PAK1 protein expression was associated with lymph node metastasis. High expression of PAK2 in mammary invasive ductal carcinomas has been associated with increased survival and resistance of breast tumor cells to chemotherapeutic agents (X. Li et al., J. Biol. Chem. 2011 286(25):2291) Squamous non-small cell lung carcinomas (NSCLCs), and head and neck squamous carcinomas have aberrant cytoplasmic expression of PAK1. (C. C. Ong et al., Proc. Nat. Acad. Sci., USA 2011 108(17):7177) Group 1 PAKs contribute to squamous NSCLC cell motility, survival and proliferation (C. C. Ong et al., Oncotarget 2011 2(6):491) and PAK2 has been linked to mitosis completion in response to various cell stimuli (M. R. Banko et al., Mol. Cell. 2011, Nov. 30, 2011)